Integrating and differential transformer



July 12, 1932. w U w 1,863,751

INTEGRATING AND DIFFERENTIAL TRANSFORMER Filed Dec. 9, l929 4Sheets-$heet 1 T T f/& 5 FIG 6 P1 2 "32 J0 yen/or.

July 12, 1932. w UT 1,866,751

INTEGRATING AND DIFFERENTIAL TRANSFORMER Filed Dec. 9. 1929 Q 4Sheets-Sheet 2 July 12, 1932. w, U-rdw 1,866,751

INTEGRATING AND DIFFERENTIAL TRANSFORMER Filed Dec. 9, 1929 4Sheets-Sheet 3 J72 ventor:

July 12, 1932. w U 1,866,751

' INTEGRATING AND DIFFERENTIAL TRANSFORMER Filed Dec. 9, 1929 4Sheets-Sheet 4 J722) efiior: MM/4m Patented July 12, 1932 UNITED STATESPATENT OFFICE WALTER FUTOW, OF FRANKFOBT-ON-THE-MAIN, GERMANY, ASSIGNORTO ELEK- TBIZITATSFACTIEN-GESELLSCHAFT VORM. LAHMEYER & 00., OFFRANKFURT-ON- THE-MAIN, GERMANY, A GERMAN COMPANY INTEGRATING ANDDIFFERENTIAL TRANSFORMER Application filed December 9, 1989, Serial No.412,894, and in Germany June 11, 1928.

It is fre uently necessary to measure the sum and difference of thecurrents assing through two or more electric con uctors. This problemhas frequently to be solved for instance when electric machines orapparatus have to be protected and the present invention provides anintegrating and differential transformer which as hereinafter describedenables the sum as well as the difference of such currents to bemeasured with one and the same transformer.

In all the figures the iron core is marked E. P signifies the primarywinding, S the secondary winding. Figure 1 refers to a-currenttransformer of usual construction. Figure 2 shows how to connect twonormal current transformers in order to measure the sum of the currentson the secondary side of the transformers. This can also .be effected byusing the connection represented in Figure 3, two normal currenttransformers being employed also. The connection shown in Figure 4enables to measure the difference of the primary currents.

The sum or the difl'erence of currents can also be established by usingspecial current transformers havin' but one core yet two primary windins. igure 5 shows a current transformer wit the primary windings P and Pbeing wound around the iron core E. The current in the secondary windingof this current transformer and the voltage V at its terminalscorresponds with the sum of the currents in the primary windings. Bychanging over the direction of current in one of the primary windingsthe connection shown in Figure 6 is obtained; with this connection thedifference of the primary currents is measured. I

Figures 7 and 8 are diagrams of the wellknown so-called differentialconnection for protective purposes that is to say a connection by meansof which the reliability of o eration in line systems etc. is secured.11 Figure 7 two normal currenttransformers are used, the iron cores ofwhich are respectively maked E and E while the secondary windings S andS are differentially connected together with a relay J thus acting whenthe currents in the primary windings H respectively R which at the sametime form the windings of a transformer A situated for instance at thebeginning of the line to be rotected differ from another. Figure 8reates to the same connection built up with special current transformersof the type shown in Figure 6. It is suggested to protect the windin sof a three phase generator G. The beginning H and the end R of eachwinding are wound on the iron cores E respective ly E respectively E ofspecial current transformers the secondar windings of which are markedrespectively S and S The windings of the generator G are connected instar by establishing an artificial zero point. Figures 9 andlO relate toa special current transformer of a type which can be used advantageouslyin the connection re resented in Figure 8. The iron core E has a ridgeSt on which a winding S is arranged the current of which'correspondswith the sum of the currents flowing through the priinaryconductorsHandR. Another winding D around the iron core E'is subdividedinto partialwindings for instance six of those windings substantially eual and connected so as to measure the di erence of the primar currentsflowing through H and R. uch a special current transformer may be namedan integratin and differential current transformer that is to say acurrent transformer forming the sum as well as the difference of primarycurrents.

Figures 11 and 12 indicate how to connect the subdivided secondarywinding D for measuring either the difference (Fig. 11) or the sum (Fig.12) of the primary currents flowing through H and B. As the additionalwinding S on the bridge St already measures the sum of the rimarycurrents the connection shown in igure 11 will be employed usually.

Figure 13 refers to particulars of the connection indicated in Figure11. The winding D consists of six partial windings in order to obtainequality of the fluxes F and F in the two parts of the iron core E. Theadditional windin S on the bridge St is likewisely subdivi ed into twoequal partial windings connected together in parallel.

For the purpose of protecting a three-phase generator three integratinand differential transformers are used, t .e primary conductors of whichmay proceed from the beginning and end of each winding of the generator.Overload relays are joined to the terminals of the windings S, whilerelays J are connected, as shown in Fig. 13.

Figure 11 illustrates that the same special current transformers can beused too if the currents to be compared with are flowing in the samedirection through the windows or openings of the special transformerthus generating the fluxes F and F the directions of which are marked byarrows.

Fig. 15 shows the transformer in Fig. 14 with subdivided windings.

The power output of the part serving for the differential measurementmay be increased by winding the primary conductors several times roundthe iron core E, as shown in Figure 16.

Figure 17 indicates how the power output of the part serving for theintegrating measurement may be increased. The primary conductor H hasbeen wound several times around the bridge St, the primary conductor Rforming but a single bar.

Figures 18 and 19 show means for increasing the total power output ofthe aforesaid special current transformers. According to Figure 18 bothprimary conductors H and R are wound around the iron core E and theprimary conductor H is furthermore wound several times around the bridgeSt. According to Figure 19 both primary conductors H and R are woundseveral times around the bridge St of the iron core E.

In Figure 1 of the accompanying drawings the iron core of a normalcurrent transformer is marked E. In the secondary winding S appears thevoltage V when the primary winding P is traversed by current.

By means of two such normal current transformers, the sum of thecurrents in the conductors P and P can be measured as indicated inFigures 2 and 3. The voltage V appearing at the terminals of thesecondary windings corresponds to the sum of the currents passingthrough the primary conductors P and P The connection shown Figure 3 isknown as an unsymmetrical connection and is used more particularly whenprotection is required from earth. leakage.

The difference between the two primary currents will be obtained bychanging over the connection of the secondary windings S and 8 Thisconnection is shown in Figure 1, concerning the employment of normallyconstructed currenttransformers. It is well known that either the sum orthe difference of currents may be measured with current transformers byconnecting in series their secondary windings. If connecting thesewindings so as to obtain counteracting of the induced electromotiveforces the resulting voltage at the secondary terminals and thesecondary current to correspond with the difference of the primarycurrents.

One iron core and one secondary winding may be utilized instead of twotransformers by carrying the primary windings P and P through the windowor opening of the iron core of a normal current transformer as shown inFigures 5 and 6, where the primary windings P and P are wound on thecore or yoke E.

The action of the connection shown in Figure 5 corresponds to that ofthe connection shown in Figure 3. Similarly the connection shown inFigure 6 corresponds to that shown in Figure 4. In the connections shown1n Figures 3 and 4 two iron cores are magnetized and the currents areelectrically integrated while in the connections shown in Figures 5 and6 the magnetic fluxes in the transformer core are correspondinglyintegrated, for only a single iron core is traversed by the integralflux. In both cases the final effect is quite the same.

The well known forms of current transformers hitherto manufactured orcurrent transformer connections referred to above are utilized formeasuring and protection purposes in single phase or polyphaseinstallations. Thus the usual transformer illustrated in Figure 1, isutilized for measur- 1ng purposes and for the feeding of maximum relays.The connections shown in Figure 3 or Figure 5 are used for protectionagainst earth leakage and those of Figures 4 and 6 in the case ofdifferential protection. The well known connections for the latter arediagrammatically shown in Figures 7 and 8; J in Figure 7 signifies adifferential current relay.

If in the case of the protection of a generator for example integratingand different-lal connections are required, an integrating anddifferential current transformer according to the present invention maybe used. Figures 9 and 10 show the construction.

' On the iron core E is arranged the wind ing D in which is measured thedifference of the currents which flowthrough the primary conductors Hand R, and the core E I is provided in the centre with a bridge St, thecross section of which depends on the purpose for which it is intendedand on which is arranged the secondary winding S, by means of which ismeasured the sum of the currents flowing through the primary conductorsH and R.

if measuring instruments are to be connect-ed to the secondary windingor coil S, the bridge St will be made of large cross section but if onthe contrary only relays are to be connected to the said winding thebridge St may be of a comparatively small cross section.

The winding D is a differential winding and is constituted by severalparallel Windings, for instance six as shown, whereby all these parallelwindings have the same num ber of spires and are distributed uniformlyover the iron core E. Such a subdivided differential winding has beennamed a push winding and its operation is well known from the theory oftransformers, especially from high tension transformer for testingpurposes. This push winding eliminates the unfavourable action of anydissymmetry of the flux tending to generate a so-called disturbancecurrent in the secondary winding. If for instance the flux at the laceof one partial winding of the push winding tends to increase 'over theflux at the places of the other partial windings a current will flowfrom the first named partial winding to all the other partial windings,connected together in parallel, whereby the first named partial windingalmost acts as a primary winding feeding a secondary winding consistingof the totality of the remaining partial windings, which therefore alsotake an increased tension and an increased current generating anadditional magnetization thus causing that all parts of the iron coreare floated by the same flux. The push winding therefore effects anuniform distribution of the magnetic flux; any local excess of themagnetic flux is almost ushed by the par tial winding directly in ucedfrom this flux to the totality of the remaining partial windings.Generall the push winding consists of a pluralit of equal coils andthese may be arranged si e by side or also partly overlap each other.When as shown in Figure 11, a current flows in the two conductors H andR in the opposite direction, two oppositely directed magnetic fluxes Fand F of equal strength will be produced in the iron core E which willcancel each other in an iron core without a bridge. Therefore, if thecurrents passing through H and R are of equal strength no electromotiveforce will be able to appear in the differential windings D and D In acurrent transformer as shown in Figures 9 and 10 the two fluxes F and Finduced by the primary currents flowing in the conductors H and R closeover the bridge St in which accordingly appears the sum of these fluxes.An electromotive force which corresponds to the sum of the currents willthere? fore appear at the terminals of the winding S which is mounted onthe bridge St, whilst the electromotive forces will cancel each other inthe secondarily connected differential windings D.

The instrument or relay J joined to the terminals of two secondarywindings D and D connected in series as shown in Figure 11 willtherefore only receive a current when the currents in the lead andreturn of the primaryconductors H and R are of different strengtAccording to Figure 12, the differential windings D and D can also beconnected in such a manner that at the terminals A and B anelectromotive force will act which corresponds to the sum of thecurrents in the primary conductors H and R.

The subdivision of the windings D and D into push windings connected inparallel is shown in Figure 13. The result of these windings is, asalready mentioned, that the flux is uniformly distributed even when theconductors H and R are not arranged symmetrically. The push winding hasthe further advantage that strange fields which are generated byconductors situated in close proximity to the transformer cannotexercise any disturbing influence. The winding S arranged on the bridgeSt, is also protected from the influence of strange dispersion fieldsowing to the fact that it is completely surrounded by the iron core E.

The integrating and differential transformer is especially qualified forthe protection of generators. In the case of a threephase generator theleads of the windings for the three phases are carried through three ofthe aforesaid integrating and differential transformers. Their ends areonly connected for establishing a control or zero point behind thetransformers. Three differential relays may be connected as shown inFigure 11. Vhen the generator is to receive a wattmetric earth leakageprotection, the current coils ofthe three required wattmetric earthleakage relays of usual construction and of any of the well known typesmay be connected in series with the coils of the aforesaid differentialrelays. The earth leakage relays receive their voltage from a voltagetransformer connected between the neutral or zero point of the machineand earth.

Due to this application, which is given merely by way of exa ple, onlythree current transformers are equired for the generator protectionwhilst hitherto it was necessaryto use at least six. The transformersmay be mounted on the terminal board of the machine where theyrequiretherefore considerably less room than those hitherto known.

When the direction of current in one of the primary windings of atransformer as shown in Fig. 11 or 12 is reversed, a connect-ion shownin'Fig. 14 will be obtained, both primary conductors being marked H inthis figure. The positions and functions of the windings D and S areexchanged as compared with Fig. 11. By means of the coil D which is nowpositioned on the bridge St, the difference of the currents in the twoconductors will then be measured, whilst electromotive forces M and U,respectively, are generated in the windings S and S in proportion to thecurrents in the windings.

Referring nowto Fig. 15,the windings on the yoke or core E at oppositesides of the bridge St are subdivided into three units each, 8,. S S atthe left, and S S S at the right. The winding on the bridge St issubdivided into two units D, D. The windings on the yoke are connectedin parallel and the windings on the bridge are in differentialconnection. The action of all units is substantially equal. Thedifferential relay J is connected to the units D.

The primary windings may as already stated be carried through the windowof the iron core or be wound round itseveral times as indicated inFigure 16.

As shown in Figure 17, one conductor may also be carried through thewindow of the iron core, whilst the other one may be wound several timesround the bridge. This arrangement, which results in more ampereturnsbecoming effective for the integrating transformer, is more particularlysuitable in case of the primary currents being relatively small. I

In the arrangement shown in Figure 18, both primary conductors are woundround the iron core E, and one of the two conductors is wound severaltimes round the bridge St.

Finally Figure 19 shows that both conductors may be wound round the ironcore E, and both carried several times round the bridge St. Due to theconnection shown in Figures 18 and 19 not only the power output of theintegrating transformer but also the power output of the differentialtransformer are considerably increased.

Having thus described my invention what I claim and desire to secure byLetters Patent is:

1. An integrating and differential current transformer comprising aplurality of primary windings, an iron core formed with two outerbranches and a central branch and provided with the usual windows,primary conductors passing through said windows, the number of the saidprimary conductors being substantially equal for each window, a windingmounted on said central branch and generating a current corresponding tothe sum of the currents passing through said primary conductors, andwindings mounted on each of said outer branches and generating currentscorresponding to the single currents passing through said primaryconductors whereby said windings on each of the outer branches beingdifferentially connected so that the resulting current on the secondaryside corresponds to the difference of the currents passing through saidprimary conductors.

2. An integrating and differential current transformer comprising aplurality of primary windings, an iron core formed with two outerbranches and a central branch and provided with the usual windows,primary conductors passing through said windows, in the same direction,a winding mounted on said central branch and generating a currentcorresponding to the difference of the single currents passing throughsaid primary conductors, and windings mounted on each of said outerbranches and generating currents corresponding to the sum of thecurrents passing through said primary conductors for the purposespecified.

3. An integrating and differential current transformer comprising aplurality of primary windings, an iron core formed with two outerbranches and a central branch and provided with the usual windows,primary conductors passing through said windows, the number of the saidprimary conductors being substantially equal for each window, a windingmounted on said central branch and generating a current corresponding tothe sum of the currents passing through said primary conductors, saidwinding on the central branch being subdivided into a plurality ofpartial windings of substantially equal action, and windings mounted oneach of said outer branches and generating currents corresponding to thesingle currents passing through said primary conductors whereby saidwindings on each of the outer branches being differentially connected sothat the resulting current on the secondary side corresponds to thedifference of the currents passing through said primary conductors.

4. An integrating and differential current transformer comprising aplurality of primary windings, an iron core formed with two outerbranches and a central branch and provided with the usual windows,primary conductors passing through said windows, in the same direction,a winding mounted on said central branch and generating a currentcorresponding to the difference of the single currents passing throughsaid primary conductors, said winding on the central branch beingsubdivided into a plurality of partial windings of substantially equalaction, and windings mounted on each of said outer branches andgenerating currents corresponding to the sum of the currents passingthrough said primary conductors for the purpose specified.

5. An integrating and differential current transformer comprising aplurality of primary windings, an iron core formed with two outerbranches and a central branch and provided with the usual windows,primary conductors passing through said windows, the number of the saidprimary conductors being substantially equal for each window, a windingmounted on said central branch and generating a current corresponding tothe sum of the currents passing through said primary conductors, andwindings mounted on each of said outer branches and generating currentscorresponding to the single currents passing through said primaryconductors whereby said windings on each of the outer branches beingsubdivided into a plurality of partial windings of substantially equalaction, connected together in parallel, the said windings on each of theouter branches being differentially connected so that the resultingcurrent on the secondary side corresponds to the difference of thecurrents passing through said primary conductors.

6. An integrating and difierential current transformer comprising aplurality of primary windings, an iron core formed with two outerbranches and a central branch and provided with the usual windows,primary conductors passing through said windows, in the same direction,awinding mounted on said central branch and generating a currentcorresponding to the difference of the single currents passing throughsaid primary conductors, and wlndings mounted on each of said outerbranches and generating currents corresponding to the sum of thecurrents passing through said primary conductors for the urposespecified, said windings on each of tiie outer branches being subdividedinto a plurality of partial win ings of substantially equal action,connected together in parallel.

7. An integrating and differential current transformer comprising aplurality of primary windings, an iron core formed with two outerbranches and a central branch and provided with the usual windows,primary conductors passing through said windows, the number of the saidprimary conductors being substantially equal for each window, a windingmounted on said central branch and generating a current corresponding tothe sum of the current passing throu h said primary conductors, saidwinding on the central branch being subdivided into a plurality ofpartial windings of substantially equal action, and windings mounted oneach of said outer branches and generating currents corresponding to thesingle currents passing through said primary conductors whereby saidwindings on each of the outer branches bein subdivided into a pluralityof partial win ings of substantially equal action, connected together inparallel, the said windings on each of the outer branches beingdifierentially connected so that the resulting current on the secondaryside corresponds to the difference of the currents passing through saidprimary conductors.

8. An integrating and difierential current transformer comprising aplurality of primary windings, an iron core formed with two outerbranches and a central branch and provided with the usual windows,primary. conductors passing through said windows, in the same direction,a winding mounted on said central branch and generating a currentcorresponding to the difference of the single currents passing throughsaid primary conductors, said winding on the central branch beingsubdivided into a plurality of partial windings of substantially equalaction, and windings mounted on each of said outer branches andgenerating currents corresponding to the sum of the currents passingthrough said primary conductors for the purpose specified, said windingson each of the outer branches being subdivided into a plurality ofpartial windings of substantially equal action, connected together inparallel.

9. An integratin and differential current transformer comprising an ironcore formed with two outer branches and a central branch and providedwith two usual windows, two primary conductors one passing through thefirst and the other through the second of said windows, one of saidprimary conductors being wound several times around said 'ccntralbranch, a winding mounted on said central branch and generating acurrent corresponding to the sum of the single currents passing throughsaid primary conductors, and windings mounted on each of said outerbranches and generating currents corresponding to the single currentspassing through said primary conductors whereby in the case ofdifierential connection the resulting current on the secondary sidecorresponds to the difierence of the currents passing through saidprimary conductors.

10. An integrating and differential current transformer comprising aniron core formed with two outer branches and a central branch andprovided with two usual windows, two primary conductors, one passingthrough the first and the other through the second of said windows, bothof said primary conductors being wound several times around said central branch, a winding mounted on said central branch and generating acurrent corresponding to the sum of the single currents passing throughsaid primary conductors, and windings mounted on each of said outerbranches and generating currents corresponding to the single currentspassing through said primary conductors whereby in the case ofdifierential connection the resulting current on the secondary sidecorresponds to the difference of the currents passing through saidprimary conductors.

11. An integrating and differential current transformer comprising aniron core formed withtwo outer branches and a central branch andprovided with the usual windows, two primary conductors one passingthrough the first and the other throughthe second of said windows in thesame direction one of said primary conductors being wound several timesaround said central branch, a

winding mounted on said central branch and generating a currentcorresponding to the difference of the single currents passing throughsaid primary conductors and windings mounted on each of said outerbranches and generating currents corresponding to the sum of thecurrents passing through said primary conductors for the purposespecified.

12. An integrating and differential current transformer comprising aniron core formed with two outer branches and a central branch andprovided with the usual windows, two primary conductors one passingthrough the first and the other through the second of said windows inthe same direction both of said primary conductors being wound severaltimes around said central branch, a winding mounted on said centralbranch and generating a current correspond ing to the difference of thesingle currents passing through said primary conductors and windingsmounted on each of said outer branches and generating currentscorresponding to the sum of the currents passing through said primaryconductors for the purpose specified.

13. An integrating and differential current transformer comprising aniron core formed with two outer branches and a central branch andprovided with the usual windows, primary conductors passing through saidwindows, said primary conductors being wound several times around saidouter branches, a winding mounted on said central branch and generatinga current corresponding to the sum of the currents passing through saidprimary conductors, and windings mountedon each of said outer branchesand generating currents corresponding to the single currents passingthrough said primary conductors whereby in the case of differentialconnection the resulting current on the secondary side corresponds tothe difierence of the currents passing through said primary conductors.

14:. An integrating and differential current transformer comprising aniron core formed with two outer branches and a central branch andprovided with the usual windows, primary conductors passing through saidwindows in the same direction, said primary conductors being woundseveral times around said outer branches, a -winding mounted on saidcentral branch and generating a current corresponding to the difi'erenceof the single currents passing through said primary conductors andwindings mounted on each of said outer branches and generating currentscorresponding to the sum of the currents passing through said primaryconductors for the purpose specified.

15. An integrating and differential current transformer comprising aniron yoke having two side bars and a central bridge signature.

WALTER BUTOW.

